Over 10% of humans suffer chronic sleep disorders, but the genetic and neural mechanisms that regulate sleep are poorly understood. The identification of defective Hypocretin/Orexin (Hcrt) signaling as a cause of narcolepsy provided a genetic entry point into sleep research, but an effective treatment for this disorder has not yet been found. Moreover, only a small fraction of sleep disorders are associated with narcolepsy, indicating that additional genes and neurons that control sleep and wakefulness remain to be identified. The objective of this proposal is to use zebrafish as a simple and cost-effective vertebrate model system to study Hcrt signaling and sleep. Zebrafish are a useful model for these studies because they have the basic brain structures and genes that are thought to regulate mammalian sleep, but are also optically transparent and amenable to high-throughput behavior assays. The proposed research has three aims. First, we will characterize the development of larval zebrafish Hcrt neurons at the single neuron level and test hypotheses about their development. Second, we will use genetic and pharmacological approaches to determine which neurons are activated by Hcrt signaling and which neurotransmitter systems are required for Hcrt-induced wakefulness. Third, we will determine whether other sleep regulators, including adenosine, melatonin, and Kv3-type potassium channels, affect sleep via the Hcrt system. These experiments will improve our understanding of Hcrt neuron development and function, may provide clues to the basis of sleep disorders such as chronic insomnia, and may lead to novel therapies for these disorders.